Many unmanned aerial vehicles include multiple motors, each having one or more propellers for generating forces in a given direction, typically in a direction corresponding to an axis of the motor, about which the propeller rotates. Many unmanned aerial vehicles feature two, four, eight or other numbers of motors and propellers to provide forces of lift and/or thrust in any number of directions. The motors and propellers may be operated independently or in concert with one another, on an as-needed or an as-desired basis. For example, because the availability of excess lift is most essential during take-off and landing (or vertical) evolutions of an unmanned aerial vehicle, multi-rotor unmanned aerial vehicles are commonly equipped with greater lift capacity than is commonly required during most transiting (or forward) operations, in order to ensure that excess lift is available when needed, primarily during take-offs or landings.
In order to conserve onboard electrical power when force is neither desired nor required from each of the motors provided aboard an unmanned aerial vehicle, one or more of the motors may be shut down from time to time, such as when the unmanned aerial vehicle is transiting, or operating in a thrust mode, or other modes in which force in a direction of a motor axis is not required. One or more of the motors may be restarted when the unmanned aerial vehicle prepares to land at a given location, or otherwise requires force in a direction of a motor axis.
A propeller that is at rest on an in-flight unmanned aerial vehicle may create undesirable drag and restrict the stability of the unmanned aerial vehicle during transiting operations. Where a propeller at rest is aligned normal to a direction of wind flow, the propeller may naturally align in a direction parallel to that of the wind flow, or be urged into that direction, thereby reducing the extent of drag created by the propeller. Where a propeller at rest is not aligned normal to the direction of wind flow, however, drag created by the propeller may be substantial.